The invention relates to suction samplers and lysimeters. The invention also relates to methods of obtaining liquid samples from wells.
As understanding of the effects of soil and water contamination advances, it is increasingly desirable to facilitate groundwater sampling and analysis. Various methods have been employed to extract a soil water sample, including extraction of a soil core, introduction of vacuum-based or absorptive devices or materials, use of suction lysimeters, solution samples, and other methods. There are several types of lysimeters including weighing lysimeters and suction lysimeters. The term xe2x80x9clysimeter,xe2x80x9d as used below, refers to a suction lysimeter.
A suction lysimeter is a hydrological instrument used to sample liquids or monitor in soil or like substrates. The lysimeter accomplishes this function by application of vacuum or pressure gradient principles such that the liquid of interest is drawn toward the lysimeter permitting collection of a liquid sample. A filter arrangement is frequently employed in conjunction with a lysimeter such that undesired particulate or other solids are not accumulated with the desired sample liquid.
A lysimeter is primarily a sampling device but can also be used to provide an indication of the water pressure (positive or negative). This is done by applying a vacuum, allowing the sampler to pressure equilibrate with the surrounding material being sampled, and then retrieving the sampler to land surface and quickly connecting to a pressure measurement device to obtain an estimate of the in situ soil water potential.
The desired sample liquid is sometimes present only in very thin layers or the material to be sampled may be unsaturated (pores are not filled to capacity with water) and it may be desired to extract liquid samples at various depths within the region of interest; this introduces the difficulty of collecting larger volume liquid samples from the borehole walls of uncased wells at intermediate depths. Another difficulty that is encountered is that the desired liquid may not be flowing freely within the soil but may be held in place by capillary forces. This condition requires the use of vacuum or hydraulic gradient forces to overcome the capillary action and secure the desired sample from its present location, be the sample region saturated or unsaturated.
Liquid sampling with a non-permanent device is performed using several techniques. An absorbent technique (sponge or filter paper) can be used, however this provides small volume samples that are often mixed (contaminated) with sediment/foreign debris.
Prior art devices utilize direct burial or insertion of lysimeter devices into direct contact with the soil region of interest. For example, U.S. Pat. No. 4,759,227 to Timmons teaches of a direct burial method at the sampling location, utilizing a backfill arrangement of bentonite and silica slurry located below, around and above the installed lysimeter. Additional detail is given by Timmons as to the preparation of filter material from a fluoroplastic resin.
In U.S. Pat. No. 4,923,333 to Timmons, the inventor reveals a leak detection scheme utilizing lysimetery at landfills and similar locations. In this case, complete contact burial of the lysimeter(s) is again disclosed.
U.S. Pat. No. 5,000,051 to Bredimeier discloses a lysimeter probe introduced into the ground via force placed upon a horizontal rod or shaft. The instrument is pressed into intimate hydraulic contact with the sediment to be sampled.
U.S. Pat. No. 5,465,628 to Timmons discloses sampling at multiple depths through the installation of a tube body into which a second mechanism may be inserted for extraction of liquids at a level coinciding with any one of several permeable zones located along the length of the installed tube.